Myth 1: An object always moves in the direction of the net force exerted on it.
When first looking at this you think, well this should be true right? Wrong! When you take a closer look here's what you get:
For this experiment we are going to focus on the time the ball is actually rolling not when it is initially pushed. So when you look at the FBD of the ball while it is in motion you will see that the net force of the ball is actually backwards even though the ball is rolling forwards.
The net force would be ΣFx = -Ff but the ball is not moving in a negative direction, it is moving in a positive direction; therefore this myth is... BUSTED!
Myth 2: An object always changes its motion if there is a force exerted on it by other objects.
Again this seems pretty reasonable, but my team of mythbusters found a way to bust this myth too.
So in this experiment, the tennis ball hit the bowling ball while it was in motion. If you look at the FBD of the bowling ball at the moment the tennis ball hits it, you see that even though there is an applied force going in the negative direction, the ball continues its motion unchanged. Although the ball might have slightly slowed down, we could not detect a detectable amount of change in motion in the ball.
Even though there is an applied force going in the negative direction, the ball continues it's path moving in the positive direction unchanged. This myth is totally BUSTED!
Neither of these two myths was too big of a challenge for our superior team of mythbusters. We couldn't prove these myths wrong completely because we lack the proper materials but based on our data (what we saw the ball do) we can loosely conclude that these myths are busted.
People believe that an object always moves in the direction of the net force exerted on it because it sounds pretty reasonable. If you push a wagon, most likely the wagon will go in the direction you pushed it, it won't randomly start going sideways or backwards. But, in some cases, the ΣF is not going in the same direction as the object. People usually believe this myth because we forget the force of friction exists, this myth would be true if friction did not exist but there is friction in our world, therefore this myth is untrue. People will also believe that an object always changes its motion if there is a force exerted on it by other objects because again, it sounds reasonable. If you push that same wagon it usually will start moving in the direction you pushed it. But if the wagon weighs 600 pounds and you only weigh 90, there is not a good chance that you will be able to get the wagon to move. So if the applied force is significantly smaller than the object then the object will not change its motion. People just don't like to think about the special cases of things, mostly they will just look at it and think hey that sounds right and not try to prove it wrong to themselves to prove themselves right. People are lazy sometimes and sometimes people just say oh that sounds right and do not bother to try it out.